Improvement of lactic acid tolerance by cocktail δ-integration strategy and identification of the transcription factor PDR3 responsible for lactic acid tolerance in yeast Saccharomyces cerevisiae.

Although, yeast Saccharomyces cerevisiae is expected to be used as a host for lactic acid production, improvement of yeast lactic acid tolerance is required for efficient non-neutralizing fermentation. In this study, we optimized the expression levels of various transcription factors to improve the lactic acid tolerance of yeast by a previously developed cocktail δ-integration strategy. By optimizing the expression levels of various transcription factors, the maximum D-lactic acid production and yield under non-neutralizing conditions were improved by 1.2. and 1.6 times, respectively. Furthermore, overexpression of PDR3, which is known as a transcription factor involved in multi-drug resistance, effectively improved lactic acid tolerance in yeast. In addition, we clarified for the first time that high expression of PDR3 contributes to the improvement of lactic acid tolerance. PDR3 is considered to be an excellent target gene for studies on yeast stress tolerance and further researches are desired in the future.

Modulation of gene expression by cocktail δ-integration to improve carotenoid production in Saccharomyces cerevisiae.

Carotenoids, including ß-carotene, are commercially valuable compounds, and their production by engineered Saccharomyces cerevisiae is a promising strategy for their industrial production. Here, to improve ß-carotene productivity in engineered S. cerevisiae, a cocktail δ-integration strategy, which involves simultaneous integration of various multi-copy genes, followed by selection of desirable transformants, was applied for modulation of ß-carotene production-related genes expression. The engineered strain, YPH499/Mo3Crt79, was constructed by three repeated rounds of cocktail δ-integration using CrtE, CrtYB, and CrtI derived from the yeast, Xanthophyllomyces dendrorhous. The recombinant strain produced 7.3 mg/L of carotenoids in 48 h and 52.3 mg/L of ß-carotene in 96 h, which were greater values than those achieved by CrtE, CrtYB, and CrtI co-overexpressing strains. Therefore, repeated cocktail δ-integration was effective in improving carotenoid productivity in S. cerevisiae and could be a promising technique for constructing metabolically engineered S. cerevisiae capable of producing bio-based chemicals.